This is what the official website says about it:
"Oscar and sister Linda now live in Tokyo. Oscar survives by doing small drug deals while Linda is a stripper in a nightclub. One night during a police raid, Oscar is hit by a bullet. While dying, his spirit, faithful to the promise made to his sister to never give up, refuses to leave the world of the living. Then his mind wanders in the city and his visions become increasingly chaotic and nightmarish. Past, present and future will mix in a hallucinatory maelstrom."
And here what the master himself got to say about it: